In a knee protecting airbag device of the prior art as disclosed in JP-A-2002-37003, which is constituted by housing a folded airbag in a case to be attached to a steering column, the case is attached to a column tube of the steering column. In this knee protecting airbag device of the prior art, the case is made of a sheet metal and attached to the column tube.
Moreover, a steering column of the prior art is constituted such that a main shaft is moved toward the front side of a vehicle along the axial direction and deforms an impact energy absorbing member when an impact acts in the forward direction, thereby absorbing the impact (or the impact energy). In case the knee protecting airbag device of the prior art is constituted such that it is attached to the main shaft of the steering column, as described above, the knee protecting airbag device moves together with the main shaft. In this case, moreover, the case made of a sheet metal which is moved may hit a member attached to a column cover which is arranged around the main shaft but does not move even at the moving time of the main shaft.